This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The ultimate inability of the immune system to eliminate cytomegalovirus (CMV) from the host is likely due to sophisticated viral evasion mechanisms that target many aspects of the host immune system. In this project, we will try to gain a better understanding of the molecular mechanisms by which CMV modulates the induction of innate immune responses, particularly the interferon response. Specific Aim 1: To identify the mechanism of IRF3 activation by HCMV It is not known how HCMV activates interferon-regulatory factor 3 (IRF3). We will identify host cell proteins that are essential for HCMV and dsDNA-dependent IRF3 activation using systematic gene knockdown by small interfering RNA (siRNA). Specific Aim 2: To determine how Hpp71, Rpp71 and Rpp65a interfere with IRF3-dependent ISG activation Fibroblasts expressing Hpp71, or infected with RhCMV, are completely refractory to IRF3 activation by HCMV as well as interferon-stimulatory DNA. The mechanism of this interference is not known and will be studied in this aim. Specific Aim 3: To characterize the role of pp65 and pp71 in controlling the innate immune response to HCMV and RhCMV We hypothesize that Rpp65a and Rpp71 inhibit the induction of innate immune response genes in RhCMV-infected cells and that Hpp71 limits their induction during HCMV infection. We will generate RhCMV mutants to test this hypothesis.